The present invention relates to an anti-wear additive for lubricating compositions and specifically to an extreme pressure, anti-wear additive.
Lubricating compositions reduce friction and reduce or prevent destructive contact between moving metal surfaces as long as a lubricating film is maintained between the moving surfaces. This particular type of lubrication is referred to as hydrodynamic lubrication.
Some anti-wear additives enhance the hydrodynamic lubrication of motor oils and the like. However, when the pressure and/or rubbing speeds between the moving metal surfaces increase, the lubricating film is forced out from between the moving metal surface. This results in metal-to-metal contact and wear. Lubrication under these extreme pressure conditions requires an additive that is adsorbed by or reacts with the metal to form an adherent protective film having a lower shear strength with the metal. This type of lubrication is needed under conditions called boundary lubrication, and additives enhancing this type of lubrication are known as "extreme pressure, anti-wear additives."
Many extreme pressure, anti-wear additives are known, with the most commercially used additives being phosphorus containing compounds, such as dialkyldithiophosphates. While these phosphorus-containing compounds provide a high degree of boundary lubrication, there is a move away from these types additives, especially for use in internal combustion engines because of the belief that, when these compounds or their oxidation products are carried by the exhaust gases, they react with and reduce the life of emission control catalysts.
Various types of other extreme pressure, anti-wear additives are known, such as the boron-containing compounds disclosed in U.S. Pat. Nos. 2,975,135; 3,509,054; 3,347,793; 3,356,707 and 4,115,286. While these boron-containing compounds provide some degree of boundary lubrication, other additives of similar or superior properties to the dialkyldithiophosphates are still being sought, and particularly those which will not poison or otherwise interfere with automotive emission control catalysts.
Certain derivatives of 2,5-dimercapto-1,3,4-thiadiazole have been disclosed as useful in lubricating compositions as corrosion inhibitors, such as the reaction product of a diamine and 2,5-dimercapto-1,3,4-thiadiazole (U.S. Pat. No. 2,910,439) and the reaction product of formaldehyde, a diaryl amine and 2,5-dimercapto,1,3,4-thiadiazole (U.S. Pat. No. 2,765,289). Other derivatives of 2,5-dimercapto-1,3,4-thiadiazole used as corrosion inhibitors in lubricating compositions are reaction products with an unsaturated ketone (U.S. Pat. No. 2,799,652); with an unsaturated cyclic compound (U.S. Pat. No. 2,764,547); and with formaldehyde and alcohol (U.S. Pat. No. 2,850,453). Also disclosed as corrosion inhibitors are thiadiazolyl dithiocarbamates (U.S. Pat. No. 2,690,999) and the carboxylic ester derivatives (U.S. Pat. No. 2,760,933).